Ch.11 Geology 1401 – Flashcards
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What does the term unconformity mean?
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a missing rock layer in a sequence that represents a period of erosion or nondeposition
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What characteristic most directly DISTINGUISHES an angular unconformity from a nonconformity?
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Angular unconformities separate rock layers along nonparallel surfaces.
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Law of superposition
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In sedimentary rocks, the rock bed on the bottom must be older than the rock bed on the top.
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Principle of original horizontality
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Sedimentary rocks were originally deposited as flat-lying, horizontal layers.
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Principle of cross-cutting relationships
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Any rock or feature, cutting through another rock or feature, must be younger than the material through which it cuts.
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Inclusions
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Any rock fragments included within another rock must be older than the rock in which they are included.
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A sandstone contains inclusions of metamorphic rock. An igneous dike cuts both the sandstone and inclusions. List the rocks from youngest to oldest.
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igneous dike, sandstone, metamorphic rock
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If a sequence of sedimentary units is cut by a fault, what does the principle of cross-cutting relationships tell a geologist?
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All of the sedimentary units must have been deposited and lithified before being cut by the fault.
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An undeformed sequence of sedimentary rocks is exposed in a large river canyon. Which two principles would be demonstrated by the rocks?
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principles of superposition and lateral continuity
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An igneous dike cuts through limestone, but not through the overlying sandstone. How did this happen?
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First, the limestone was laid down, then intruded by the igneous dike, and lastly the sandstone was deposited.
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Following the deposition of a sequence of sedimentary rocks, which event is the first to occur to produce an angular unconformity?
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deformation
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A __________ exhibits sedimentary layers that are parallel to each other above and below an erosive surface.
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disconformity
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An accurate description of a nonconformity?
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younger sedimentary strata overlie uplifted and weathered igneous or metamorphic rocks
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The sedimentary layers above an erosive surface are __________ relative to all rocks present below the surface.
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younger
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A common feature that all unconformities exhibit?
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erosive surface
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What is the category name for the largest division of time used on the geologic time scale?
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Eon
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Why is the geologic time scale more detailed in the Phanerozoic than in previous eons?
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The Phanerozoic Eon is more detailed because of the presence of organisms with hard parts and the rapid increase in biodiversity.
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The Jurassic Period lies in the _____ Era, which was dominated by large terrestrial vertebrates, or _____.
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Mesozoic; dinosaurs
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Using a calendar year as an analogy to the geologic time scale, when do the oldest anatomically modern humans appear on Earth?
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The oldest human fossils show up at about eleven minutes to midnight on December 31st.
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Name the epoch, period, era and eon in which we currently live.
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We live in the Holocene Epoch of the Quaternary Period, which is part of the Cenzoic Era and Phanerozoic Eon.
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Definition of fossil range
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The period of time when an organism first and last appears in the sedimentary record.
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A characteristic most desirable for constraining the relative age of rocks?
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organisms with overlapping ranges and geologically short lifespans
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If a rock contains ten different kinds of fossils, which of the following must be true?
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All of the organisms had to be alive when the rock was deposited.
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How is the geologic time scale related to the fossil record?
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The periods of the time scale were constructed based on ranges of fossil organisms.
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The fundamental principle of geology put forth by James Hutton is called _______.
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the principle of uniformitarianism
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What hypothesis promoted the view that Earth has been shaped largely by sudden, drastic events over a very short period of time?
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catastrophism
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Which principles are key to relative dating?
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-principle of cross-cutting relationships
-law of superposition
-principle of original horizontality
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3 types of unconformities
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-disconformity
-angular unconformity
-nonconformity
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Which of the following is an example of a trace fossil?
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-COPROLITES
-skull
-teeth
-shells
-claws
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What is the difference between a mold and a cast?
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Molds reflect the shape of an organism; casts fill in the molds.
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What two special conditions are necessary to preserve organisms as fossils?
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rapid burial and hard parts
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A radioactive isotope used to date very recent events
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carbon-14
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What subdivision of the geologic time scale represents the greatest expanse of time?
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Eon
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What is the best method to determine a numerical age for a sedimentary rock?
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Date surrounding rock layers, such as igneous rocks.
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What is the primary problem in assigning numerical dates to rocks?
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Not all rocks can be dated by radiometric dating methods.
